1. Field of the Invention
The present invention relates to a high-speed responsive power supply for use in measuring equipment, for example, in a test head of an IC (integrated circuit) tester disposed with a specific distance apart from the tester body rack containing a controller and a power supply, and the potential difference between the input and the output of the high-speed responsive power supply is designed to be minimized.
2. Description of the Related Art
In a known IC tester, the test head is placed in use about 10 m apart from the tester body rack containing the controller and the power supply. FIG. 6 is a block diagram showing a schematic construction of a conventional IC tester. In FIG. 6, inside an IC tester body rack 1, a transformer 2 is provided which transforms the voltage of an AC power supply 3 into a specific voltage to be applied to a remote sensing power supply 4.
The output terminal of the remote sensing power supply 4 is connected to a test head 8 placed a distance L of about 10 m apart therefrom via a voltage detecting line 6 and a feeder line 7. The output voltage of the remote sensing power supply 4 is supplied to the test head 8 through the feeder line 7. The voltage supplied to the test head 8 is detected through the voltage detecting line 6.
The voltage supplied to the test head 8 (hereinafter, referred to as power supply voltage V1) is applied to a device under test 9 (hereinafter, referred to as DUT) through a feeder line 11. A condenser 10 inside the test head 8 is a power supply bypass condenser for the DUT 9 that serves to lower the AC impedance of the power supply inside the test head 8.
Next, the performance of FIG. 6 will be described. An AC voltage is supplied from the AC power supply 3 to the transformer 2 inside the test body rack 1, and the AC voltage is transformed into a specific voltage by the transformer 2 to be supplied to the remote sensing power supply 4. The voltage rectified and stabilized by the remote sensing power supply 4 is supplied to the test head 8 through the feeder line 7.
Thus, the power supply voltage V1 is applied to the DUT 9 mounted on the test head 8 through the feeder line 11, and thereby a power supply current I1 is fed into the DUT 9. Here, the current is about 1.about.3 A depending on the DUT 9, and therefore, the voltage fed to the test head 8 from the remote sensing power supply 4 fluctuates.
In order to eliminate this fluctuation, the remote sensing power supply 4 detects the voltage fed to the test head 8 through the voltage detecting line 6. Consequently, a power supply voltage with an error of less than 10 mV can be fed to the DUT 9 via the feeder line l1.
However, in the power supply for the IC tester provided with the remote sensing power supply 4 that has such a voltage detecting line 6 for control of the power supply voltage V1, when the current running through the DUT 9 changes instantaneously by about 1.about.3 A, the fluctuation of the power supply voltage V1 on the feeder line l1 cannot unavoidably be eliminated.
FIG. 7 illustrates the waveforms of the transient characteristics of the power supply voltage V1 applied to the DUT 9 and the power supply current I1 running through the DUT 9, which are shown by taking on the horizontal axis to represent time (.mu.s) and the vertical axis to represent the power supply voltage V1 and the power supply current I1.
As clearly seen in FIG. 7, when the power supply current changes instantaneously from 1 A to 3 A, the power supply voltage V1 changes about 2 V in 10 microseconds.
The fluctuation of the power supply voltage V1 accompanied with the change of the power supply current I1 can be reduced to some extent by adjusting the constant (value) of the condenser 10 in the power supply for the test head 8 and by adjusting the operational condition of the sensing power supply 4. However, the voltage fluctuation of about 1.about.3 V for the microseconds shown in FIG. 7 invariably appears, and has not been avoided in the conventional system.